Add GruntJS and NPM to support Travis-CI

Instructions from the brackets root directory:

```
> npm install -g grunt-cli
> npm install // REQUIRED! installs grunt, grunt-contrib-* dependencies, generates src/config.json (replaces old src/package.json)
> grunt jshint  // runs JSHINT on a subset of .js source files in /src and /test
> grunt jasmine // runs a subset of Jasmine specs that run without modification in PhantomJS
> grunt test --force // runs both jshint and jasmine
```

Travis-CI project page: https://travis-ci.org/adobe/brackets. Note that the builds are "failing" now because there are a number of JSHINT errors. This is expected and my hope is to merge this pull request first and follow up with another to fix the JSHINT errors after the initial kinks are worked out with Travis-CI

``package.json`` was moved to the root of the repo. This was done to use the correct conventions with NPM. A new config.json replaces the old src/package.json. The grunt script merges package.json and src/brackets.config.json into a config.json that is read at runtime to populate various metadata and other configuration options.